1. Field of the Invention
The present invention relates, in general, to a method for confirming an optimum focus of a stepper in the fabrication of semiconductor device and, more particularly, to taking advantage of the change of the line width of a photoresist pattern with the position of the focus of the light to which the photoresist pattern is exposed at a predetermined exposure energy, thereby confirming an optimum focus.
2. Description of the Prior Art
When the fabrication of a semiconductor device is carried out by a lithography process, it is reasonable that the accurately precise transcription of the image of a reticle upon the photoresist film formed on a wafer is necessary to give a desired photoresist pattern. For this, accurate information concerning how images are formed in accordance with steppers is required, and this work is usually recognized as the confirmation of an optimum focus.
Conventionally, in order to confirm an optimum focus, photoresist patterns which are the same in dimension and shape, e.g. hole or bar, are formed on a test wafer by difference in offset value. Since the photoresists are, then, examined with an optical microscope. At this time, an offset value is detected from the pattern which looks to be optimally shaped.
This conventional method, however, has a serious problem in that differences may occur according to the resolution power of the optical microscope and to the investigators.